Will we ever be able to cross the universe with the ease of the Enterprise?
Astronomer Royal Martin Rees explores the science behind the fiction

The best sciencefiction, from H G Wells onwards, can nourish everyone’s imagination. It can widen the perspective of astronomers too – that strange breed of which I’m a member. Many of us are avid consumers of the genre – though I think we’d expect aliens, if they exist, to be far stranger, and far less humanoid, than those portrayed in Star Trek. Indeed, possibilities once in the realms of science fiction have shifted into serious scientific debate – “cyborgs” and “post-humans”, alien life, and even parallel universes.

The stupendous time spans of the evolutionary past are now part of common culture (though maybe not in the United States Bible Belt, nor in parts of the Islamic world). Most people are at ease with the idea that our present biosphere is the outcome of four billion years of Darwinian evolution. But the even longer time-horizons that stretch ahead – familiar to every astronomer – haven’t permeated our culture to the same extent. Our Sun is less than halfway through its life. It formed 4.5 billion years ago, but it’s got six billion more before the fuel runs out. It will then flare up, engulfing the inner planets and vaporising any life that might then remain on Earth. But even after the Sun’s demise, the expanding universe will continue – perhaps for ever – destined to become ever colder, ever emptier. To quote Woody Allen, “eternity is very long, especially towards the end.”

Scientific forecasters have a dismal record. One of my predecessors as Astronomer Royal said, as late as the Fifties, that space travel was “utter bilge”. Few in the mid-20th century envisaged the transformative impact of the silicon chip or the double helix. The iPhone would have seemed magical even 20 years ago. So, looking even a century ahead, we must keep our minds open, or at least ajar, to what may now seem science fiction. Some proponents of the “singularity” – the takeover of humanity by intelligent machines – claim this transition could happen within 50 years.

China has become the first country to make a soft lunar landing since 1976

The Soviet Sputnik was launched in 1957. Four years later, Yuri Gagarin was the first human to go into orbit. Eight years after that, and only 66 years after the Wright brothers’ first flight, Neil Armstrong made his “one small step”. The Apollo programme was a heroic episode. Yet since 1972, humans have done no more than circle the Earth in low orbit – more recently, in the international space station. This has proved neither very useful nor very inspiring. On the other hand, space technology has burgeoned – for communication, environmental monitoring, satnav and so forth. We depend on it every day. And unmanned probes to other planets have beamed back pictures of varied and distinctive worlds.

Had the momentum of the Sixties been maintained over the next 40 years, there would be footprints on Mars by now. But after Apollo the political impetus for manned space flight was lost. This was one of many instances of the widening gap between what could be achieved technologically, and what is actually done. As with many technical forecasts, we can be more confident of what could happen than of how soon it will happen.

Development of supersonic airliners, for instance, has languished (Concorde having gone the way of the dinosaurs); in contrast, the sophistication and worldwide penetration of internet and smartphones advanced much faster than most forecasters predicted.

Nasa’s manned programme, ever since Apollo, has been impeded by public and political pressure, and is too risk-averse. The space shuttle failed twice in 135 launches. Astronauts or test pilots would willingly accept this risk level, but the shuttle had, unwisely, been promoted as a safe vehicle for civilians. So each failure caused a national trauma and was followed by a hiatus while costly efforts were made (with very limited effect) to reduce the risk still further.

Commander Chris Hadfield on the International Space Station

Unless motivated by pure prestige and bankrolled by superpowers, manned missions beyond the Moon will need perforce to be cut-price ventures, accepting high risks – perhaps even “one-way tickets”. These missions will be privately funded; no Western governmental agency would expose civilians to such hazards. There would, despite the risks, be many volunteers – driven by the same motives as early explorers, mountaineers, and the like. Private companies already offer orbital flights. Maybe within a decade adventurers will be able to sign up for a week-long trip around the far side of the Moon – voyaging farther from Earth than anyone has been before (but avoiding the greater challenge of a Moon landing and blast-off). Dennis Tito hopes that a voyage around Mars (though not landing) could be achieved in the 2020s. And Elon Musk, the visionary head of SpaceX, hopes to land on Mars himself.

(The phrase “space tourism” should however be avoided. It lulls people into believing that such ventures are routine and low-risk. And if that’s the perception, the inevitable accidents will be as traumatic as those of the space shuttle were. Instead, these cut-price ventures must be “sold” as dangerous sports, or intrepid exploration.)

I’d venture a confident forecast that during this century the entire solar system – planets, moons and asteroids – will be explored and mapped by flotillas of tiny robotic craft. The next step would be space mining and fabrication. (And fabrication in space will be a better use of materials mined from asteroids than bringing them back to Earth.) The Hubble telescope’s successors, with huge gossamer-thin mirrors assembled under zero gravity, will further expand our vision of stars, galaxies and the wider cosmos.

M74: an island universe of about 100 billion stars, 32 million light-years away

But don’t ever expect mass emigration. Nowhere in our solar system offers an environment even as clement as the Antarctic or the top of Everest. Space doesn’t offer an escape from Earth’s problems. And even with nuclear fuel, the transit time to nearby stars exceeds a human lifetime. Interstellar travel is therefore, in my view, an enterprise for post-humans, evolved from our species not via natural selection but by design. They could be silicon-based, or they could be organic creatures who had won the battle with death, or perfected the techniques of hibernation or suspended animation.

A sustained, if not enhanced, rate of innovation in biotech, nanotech and in information science could lead to entities with superhuman intellect within a few centuries. A century or two from now, there may be small groups of pioneers living independent from the Earth – on Mars or on asteroids.

What about travel beyond our solar system? Even the nearest stars are so far away that no present technology could reach them. The first voyagers to the stars will be creatures whose life cycle is matched to the voyage: the aeons involved in traversing the galaxy are not daunting to immortal beings. By the end of the third millennium, travel to other stars could be technically feasible. But would there be sufficient motive?

Would even the most intrepid leave the solar system? We can’t predict what inscrutable goals might drive post-humans. But the motive would surely be stronger if it turned out that many stars were orbited by planets that might harbour life.

How bright are the prospects that there is life out there already? There may be simple organisms on Mars, or remnants of creatures that lived early in the planet’s history; and there could be life, too, in the ice-covered oceans of Jupiter’s moons Europa and Ganymede. But few would bet on it; and certainly nobody expects a complex biosphere in such locations. For that, we must look to the distant stars – far beyond the range of any probe we can now construct.

Reflection nebulae shine because of a light source embedded within, like a street lamp illuminates fog

In the past 20 years (and especially in the past five) the night sky has become far more interesting, and far more enticing to explorers, than it was to our forebears. Astronomers have discovered that many stars – perhaps even most – are orbited by retinues of planets, just like the Sun is. These planets are not detected directly. Instead, they reveal their presence by effects on their parent star that can be detected by precise measurements: small periodic motions in the star induced by an orbiting planet’s gravity, and slight recurrent dimmings in a star’s brightness when a planet transits in front of it, blocking out a small fraction of its light.

But do we expect alien life on these extrasolar planets? We know too little about how life began on Earth to lay confident odds. And it might be too anthropocentric to limit attention to Earthlike planets.

Science fiction writers have other ideas – balloon-like creatures floating in the dense atmospheres of Jupiter-like planets, swarms of intelligent insects, nanoscale robots etc. We should be mindful that seemingly artificial signals could come from super-intelligent (though not necessarily conscious) computers, created by a race of alien beings that had already died out. Maybe we will one day find ET.

If we do find ET, we will at least have something in common with them. They may live on planet Zog and have seven tentacles, but they will be made of the same kinds of atoms as us. If they have eyes, they will gaze out on the same cosmos as we do. They will, like us, trace their origins back to a “big bang” 13.8 billion years ago. But is that all there is to physical reality?

Will we find intelligent life - or will intelligent life find us?

We are well aware that our knowledge of space and time is incomplete. What we’ve traditionally called “the universe” – the aftermath of “our” big bang – may be just one island, just one patch of space, in a perhaps-infinite archipelago. There may have been an infinity of big bangs, not just one. Each constituent of this “multiverse” cooled down differently, ending up governed by different laws. Just as Earth is a very special planet among zillions of others, so – on a far grander scale – our big bang was also a very special one.

In this hugely expanded cosmic perspective, the laws of Einstein and the quantum could be mere parochial bylaws governing our cosmic patch. Space and time may have a structure as intricate as the fauna of a rich ecosystem, but on a scale far larger than the horizon of our observations. Our current concept of physical reality could be as constricted, in relation to the whole, as the perspective of the Earth available to a plankton whose “universe” is a spoonful of water.

And that’s not all – there is a final disconcerting twist. Post-human intelligence will develop hypercomputers with the processing power to simulate living things – even entire worlds. Perhaps advanced beings could use hypercomputers to surpass the best “special effects” in movies or computer games so vastly that they could simulate a world, fully, as complex as the one we perceive ourselves to be in. Maybe these kinds of super-intelligences already exist elsewhere in the multiverse – in universes that are older than ours, or better tuned for the evolution of intelligence. What would these super-intelligences do with their hypercomputers? They could create virtual worlds vastly outnumbering the “real” ones. So perhaps we are “artificial life” in a virtual universe.

It is remarkable that our brains, which have changed little since our ancestors roamed the African savannah, have allowed us to understand the counterintuitive worlds of the quantum and the cosmos. But some of these insights may have to await post-human intelligence. There may be phenomena, crucial to our long-term destiny, that we are not aware of, any more than a monkey comprehends the nature of stars and galaxies.